The tRNAs for Asp, Asn, His and Tyr contain the hypermodified purine known as queuine in the first or wobble position of their anticodons (always position 34). However, the original transcripts of these tRNAs contain a guanine in this position. An enzyme catalyzing the excision of this guanine and replacing it with queuine has been discovered and purified to homogeneity. However, the physiological role of queuine for higher mammals remains obscure. The tRNAs of germfree mice maintained on a chemically defined diet totally deficient in queuine do not contain queuine indicating that the mouse, and probably most higher mammals, cannot synthesize queuine. Only the undermodified isoacceptor tRNA with guanine rather than queuine at position 34 was present in the liver and other organs of these mice. It was necessary to carry out this study in the germfree state since we previously showed that queuine could be supplied by the intestinal flora. No observations characteristic of a nutritional deficiency, such as weight loss, alopecia, neuromuscular symptomology, were observed. There is preliminary evidence that these mice have a diminished rate of reproduction. The purpose of this grant is to document this diminished reproductive capacity and to determine its cause; e.g. is it due to a decrease in numbers of pregnancies, live fetuses, increased number of resorbed fetuses or still births? The germfree animal lives a charmed life where there is no challenge from microorganisms, parasites or viruses. We plan to test the integrity of the immune system of the queuine-deficient mouse, and will determine if the queuine-deficient mouse has an increased susceptibility to viral challenge. Since we have established that there is a dietary requirement for queuine, we also plan to determine how queuine is transported from the gut via the blood to the cells where it is incorporated into tRNA. Another part of this project will be to determine which component(s) of the intestinal flora provide queuine. Also, there is abundant evidence that tumor cells have decreased amounts of queuine-containing tRNA. However, it is not known whether this is a cause or effect of neoplasia. Therefore, we intend to compare the incidence, type and time of onset of neoplasms in queuine-deficient mice and their counterparts that have adequate dietary queuine.